In the recent development of semiconductor fabrication technology, the continuous miniaturization in IC devices demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 .mu.m range, a cleanliness class of 100.about.1000 (which indicates the number of particles at sizes larger than 0.5 .mu.m per cubic foot of air) was sufficient. However, when the feature size is reduced to 0.25 .mu.m, a cleanliness class of 0.1 is required. It has been recognized that an inert mini-environment may be the only solution to future fabrication technologies when the device size is further reduced. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness mini-environment that is constantly flushed with ultrapure nitrogen that contains no oxygen or moisture.
Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI (ultra-large-scale-integrated) technology. One approach is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM (dynamic random access memory) products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered.
The stringer requirement requires a new mini-environment concept. Within the enclosure of the mini-environment of a process tool,, an extremely high cleanliness class of 0.1 (which means the number of particles at sizes larger than 0.1 .mu.m per cubic foot of air) is maintained, when compared to a cleanliness class of 1000 for the overall production clean room area. In order to maintain the high cleanliness class inside the process tool the loading and unloading sections of the process tool must be handled automatically by an input/output device such as a SMIF (standard mechanical interfaces) apparatus. A cassette of wafer can be transported into the process tool by a SMIF pod situated-on top of the SMIF apparatus.
In a typical SMIF transfer system, an automated loading/unloading (ALU) apparatus is normally used in conjunction with the SMIF. One of such automatic loading/unloading apparatus is shown in FIG. 1. The ALU apparatus 10 is used for transporting a wafer cassette into a wafer pod and a process machine. The ALU apparatus 10 is constructed of a port plate 12, a port door 14, a cassette support 16 and a remote switch or foot operated switch 20. On top of the port door 14, a plurality of locating pins 22 are normally provided for the proper positioning of a wafer cassette on the port door 14. The locating pins 22 are important such that an accurate positioning of a wafer cassette on the port door 14 can be assured. Improperly positioned wafer cassette on the port door 14 may accidentally fall off the port door and thus cause severe breakage problems to the wafers. The cassette support 16 has a generally, laterally extending surface 26 designed in a special contour for matching to the side contour of a wafer cassette, as shown in FIG. 1. The movable port door 14 is used to unload a wafer cassette from a pod (not shown) positioned on the fixed port plate 12.
In a normal operation, the function of the ALU apparatus 10 is to deliver a wafer cassette in or out of a wafer pod (not shown) or a process chamber (not shown). For instance, a pod (not shown) can be positioned on the port plate 12 which is equipped with two sets of latch pins. The latch pins can be operated to release the pod door such that the pod door and the cassette are separated from the pod body. When the port door 14 is moved down by an elevator to a lower position, the pod door and the cassette are lowered with the port door 14. The operation of the port door 14 can be advantageously controlled by the remote or foot operated switch 20 which provides convenient remote control of the operation of the ALU apparatus 10.
The operation of the port door 14 and the cassette support 16 is shown in detail in FIGS. 2A and 2B. The port door 14 is constructed on top of a mounting box 28 as its top surface. The mounting box 28 is also constructed by a port cover 30 which contains a cavity 32 therein forming a slot opening. The port cover 30 for the mounting box 28 further includes an opening 36 facing downwardly allowing a drive means 38 to be integrally attached to a sliding block 40. The drive means 38 can be advantageously fabricated as a pin for easy adaptation to an exterior drive system (not shown) such that the drive means 38, and subsequently the sliding block 40, can be moved in a horizontal position to a maximum displacement which is equal to the length of the opening 36. At the right end 42 of the sliding block 40, a connecting plate 44 is connected pivotally through a first connecting pin 46 therethrough. At the opposite end of the connection plate 44, a connecting rod 50 is pivotally connected by a second connecting pin 52.
In order for the connecting rod 50 to rotate the cantilever arm 54 and the cassette support plate 56, the connecting rod 50 is fixed to the mounting box 28 through an aperture 62 by a third connecting pin 64. The fluid connecting pin 64 is attached to the end panels (not shown) of the mounting box 28. To control the movement of the cassette support plate 56 accurately, the connecting rod 50 must be rigidly attached to the cantilever arm 54. This is accomplished by a mechanical means, such as a bolt 58 shown in FIG. 2A and 2B. At the other end of the cantilever arm 54, the cassette support plate 56 is attached thereto by mechanical means, such as bolts 68. It should be noted that while the cassette support plate 56 is shown with a flat surface 66, the surface 66 is more likely contoured to match the contour of a wafer cassette in a lateral direction. The length of the cantilever arm 54 can be suitably adjusted, so are the lateral dimensions of the cassette support plate 56, such that different sized wafer cassettes may be carried and supported (or cradled) by the cassette support plate 56 when placed in an upright position on top of the port door 34.
A detailed drive mechanism for the cassette support plate 56 is shown in FIG. 2B. The main drive system for the cassette support plate 56 consists of a sliding block 40, connecting plate 44 and connecting rod 50. The sliding block 40 is an elongated block constructed of a rigid material. It is housed in a mounting box 28 constructed of a port cover 30 and a port door 34. The port cover 30 is assembled, with the sliding block 40 housed therein, to the port plate 34 by mechanical means such as bolts 68. The port cover 30 and the port plate 34 are constructed of a rigid material such as aluminum or other suitable metal such that the integrity of the mounting box 28 is ensured. The rigidity of the mounting box is important in order for the sliding block 40 to slide smoothly inside cavity 32 of the mounting box 28. As shown in FIG. 2A, the sliding block 40 is mounted in a horizontal position and is allowed to move only in a horizontal direction. The mounting block 40 is equipped, at the left end 48, with a drive means 38. The drive means 38, as shown in FIG. 2A, is a simple pin device that can be engaged by an external drive means (not shown) such as that of a SMIF loader. The drive means 38, when engaged by the external drive means, moves the sliding block 40 in a horizontal direction to the right until the opposite end 60 is stopped by the surface 70 of the end wall 72 of the port cover 30.
At the opposite end 60 of the sliding block 40, a connecting plate 44 is pivotally connected by pin 46 through an aperture (not shown) in the sliding block 40. At the other end of the connecting plate 44, a second connecting pin 52 is used to pivotally connect the connecting plate 44 to the upper end 74 of the connecting rod 50. The connecting rod 50 is pivotally connected at the upper end 74 through an aperture 64 by a third connecting pin 62. The third connecting pin 62 is further attached to the end walls (not shown) of the port cover 30. The third connecting pin 62 allows the connecting rod 50 to swing on an axis provided by the third connecting pin 62. The swinging motion of the connecting rod 50, as shown in FIGS. 2A and 2B, is designed such that when the mounting block 40 is pushed by the connecting rod 50 (through the connecting plate 44) to a left-most position, the connecting rod 50 is in a perpendicular position to the longitudinal axis of the sliding block 40. On the other hand, when the sliding block 40 is pushed to the right-most position, as shown in FIG. 2B, by the drive means 3 8 and an exterior drive means such that the end 60 of the sliding block 40 is stopped by the end wall 70 of the port cover 30, the connecting rod 50 swings on the third connecting pin 62 when pushed by the connecting plate 44 to a position that is horizontal to the longitudinal axis of the sliding block 40.
When the sliding block 40 is pushed to the right-most position, as shown in FIG. 2B, the connecting plate 44 is perpendicular to the longitudinal axis of the sliding block 40. Ideally, when the connecting plate 44 and the longitudinal axis of the sliding block 40 are in a 90.degree. relationship, the connecting plate/sliding block assembly is in a self-locked position. In other words, even if a vertically downward force is applied onto the cassette support 16, the force acting in a perfectly vertical direction on the first connecting pin 46 and therefore, there is no horizontal component of the force to cause the sliding block 40 to move horizontally. However, this ideal situation does not exist in real life due to a variety of reasons. For instance, the manufacturing process for the sliding block allows a small tolerance in its dimensions, and secondly, there may have been wear on the surface of the sliding block 40 after prolonged usage of the loader/unloader apparatus. Furthermore, any vibration of the loader/unloader apparatus may cause the sliding block to move away from the position where the connecting plate 44 is in a perfect 90.degree. angle to the longitudinal axis of the sliding block 40. For instance, the sliding block 40 may be moved slightly to the left and thus causing a non-perfect vertical force to act on the first connecting pin 46 when a vertical downwardly force is applied on the cassette support 16. The non-perfect vertical force acting on the first connecting pin 46 thus produces a horizontal component of the downward force and causing the sliding block 40 to move to the left away from the perfectly perpendicular position shown in FIG. 2B. This new position is shown as ghost lines 74. At such a position, the self-locking function which existed when the connecting plate 44 and the sliding block 40 were in perfectly perpendicular position non longer exists. As a result, the cassette support 16 may swing downwardly in a clockwise direction causing the wafer cassette to slide off the port door 34. This is a serious problem which may lead to wafer breakage and thus a severe drop in wafer yield from the process machine.
It is therefore an object of the present invention to provide a support mechanism for laterally supporting an article on a platform that does not have the drawbacks and shortcomings of the conventional support systems.
It is another object of the present invention to provide a support mechanism for laterally supporting an article on a platform by utilizing a stabilizing means that can be easily added to an existing apparatus.
It is a further object of the present invention to provide a support mechanism for laterally supporting an article on a platform that provides a self-locking function when the support mechanism is in an upright position.
It is another further object of the present invention to provide a self-locking support assembly that utilizes a tension means such that when the support member is in an upright position, the tension means is in a relaxed state for stabilizing the upright position of the support member.
It is still another object of the present invention to provide a self-locking support assembly by utilizing an extensible spring means such that when the support member is in an upright position, the extendable spring means is in a relaxed state for stabilizing the upright position of the support member.
It is yet another object of the present invention to provide a self-locking support assembly by utilizing a compression means such that when the support member is in an upright position, the compression means is in a relaxed state for stabilizing the upright position of the support member.
It is still another further object of the present invention to provide a stabilized support assembly that utilizes a compression means for stabilizing a support member such that when the support member is in an upright position, the compressible spring is in a relaxed state for stabilizing the upright position of the support member.
It is yet another further object of the present invention to provide a self-locking support assembly utilizing an extensible spring for stabilizing a cassette support plate for supporting a wafer cassette situated on a port cover in a lateral direction.